For inference, we perform beam search with beam size of 4 for decoding. As the Clotho dataset has 5 reference captions for each audio, we follow the COCO image captioning evaluation process [1]} to evaluate the generated caption. The BLEUn scores [2]} calculates the degree of n-gram overlap between the generated and reference caption. ROUGEL [3]} measures the longest common sequence and gives a score base on the similarity. METEOR [4]} is said to better correlate with human annotators and uses a harmonic mean of unigram precision and recall to score the generated sequence.
CIDEr [5]} also measures similarity using the average cosine similarity between the candidate sentence and the reference sentences. Like METEOR, SPICE [6]} is also said to correlate with human judgement more by using semantic propositional content and is less reliant on n-gram overlaps. Finally, SPIDEr [7]} is a linear combination of both SPICE and CIDEr. We use all the aforementioned metrics for evaluation.
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